Keywords:Hydraulic/Pneumatic Actuators, Additive Manufacturing, Mechanism DesignAbstract: With regard to future robotic systems, the combination of Additive Manufacturing (AM) and pneumatic actuation yields multiple opportunities. Bellows actuators are exceptionally suitable for AM as the required geometrical complexity can easily be obtained and their functionality is not affected by rough surfaces and small dimensional accuracy. In this paper, multi-material PolyJet printable linear bellows actuators are presented. A design strategy based on finite elements analysis and numerical shape optimization is proposed and validated by experimental testing under quasi-static and repeated loading conditions. The presented results are useful for researchers and engineers considering the application of AM soft material bellows actuators for robots and other dynamic systems.

Keywords:Hydraulic/Pneumatic Actuators, Mechanism Design, Material Science for Soft RoboticsAbstract: In this paper, we present an improvement to a recently developed thermally responsive silicone-based actuator.The actuator is made of silicone with dispersed solvent droplets and expands when the droplets undergo a liquid-gas phase transition, which is achieved at low voltages using an embedded Joule heater. In previous work, the embedded heater was a nickel-chromium spiral-shaped Joule heating wire. In the present work, we replace the wire with a silicone-based conductive composite to create a fully soft actuator. We characterize the thermal response of the conductive composite for Joule heating the actuator and the blocked force of the actuator when implemented as a McKibben-like muscle. From this, we show that the conductive composite performs as well as the original wire heater, with improved material compatibility. Finally, we demonstrate a 20 g silicone actuator embedded with the conductive composite lifting its 4.3 kg DC power source.

Keywords:Additive Manufacturing, Flexible Robots, Hydraulic/Pneumatic ActuatorsAbstract: Additive manufacturing has a wide range of applications and addresses many challenges inherited from conventional molding techniques such as human error, multi-step fabrication, and manual handling. However, 3D printing soft functional robots with two-part platinum cure silicones requires development to match the material performance of the molded counterparts. In this paper, we present a custom 3D printer and an extrusion mechanism capable of 3D printing soft functional robots. Moreover, we compare the performance differences between our 3D printed soft robots and molded counterparts via lamination casting and lost wax casting. We validate our results by conducting multiple experiments such as blocked force, bend angle, failure pressure, and dimensional quality analyses. We demonstrate that our method enables 3D printing of soft robots that can perform better, or match the performance of molded counterparts while being more reliable and robust with the usage of the same materials.

Keywords:Soft Robot Locomotion, Flexible Robots, Soft Gripper and End-EffectorsAbstract: This paper presents the design of a planar, low profile, multi-directional soft crawling robot. The robot combines soft electroactive polymer actuators with compliant electroadhesive feet. A theoretical model of a multi-sector dielectric elastomer actuator is presented. The relation between actuator stroke and blocking force is experimentally validated. Electrostatic adhesion is employed to provide traction between the feet of the robot and the crawling surface. Shear force is experimentally determined and forces up to 3N have been achieved with the current pad design. A 2D multi-directional gait is demonstrated with the robot prototype. Speeds up to 12mm/s (0.1 body-lengths/s) have been observed. The robot has the potential to move on a variety of surfaces and across gradients, a useful ability in scenarios involving exploration.

Keywords:Soft Robot Locomotion, Simulation and AnimationAbstract: Soft body locomotion can enable mobile robots that are compliant to their surroundings. To better understand earthworm-inspired locomotion, recent robots such as our Compliant Modular Mesh Worm Robot with Steering (CMMWorm-S) have been developed. For straight-line locomotion, we have shown that balancing segment extension and retraction to mitigate slip determines control wave strategy. However, to effect a turn, the waves required to eliminate slip are more complicated because they are not periodic but rather change for each segment and for each wave. Here, we geometrically prove that the body cannot be reoriented to a new straight configuration facing a new direction in a single wave without slip and that only if the body is a constant, uniform curvature will periodic control waves not require slip. The segments are represented as isosceles trapezoids in order that the model be generalizable over other types of worm-like robots that embody a positive correlation between diameter reduction and length extension. Examples of simulated orthogonal turns are provided that are motivated by slippage in orthogonal turns demonstrated on our soft robot. Future work will involve calibrating Slip Eliminating Control (SEC) to mitigate slip on the robot.

Keywords:Soft Robot Locomotion, Flexible RobotsAbstract: In this paper, we report a paper-based wall-climbing robot capable of climbing vertical walls of different materials. The robot, made from paper and shape memory alloy (SMA), can be controlled to climb walls under certain combinations of activation patterns of electrostatic adhesion and contraction of the SMA. Electrostatic adhesion is applied using a paper structure with embedded interdigitated electrodes. This structure, fully compatible with the paper-based robot, is able to output strong and reliable adhesion forces (the resultant friction force can be as high as 1.65 N on specific substrates), and can be easily turned on and off using a commercial high-voltage converter. The SMA embedded in the robot is employed to deform the robot body and induce contracting displacements while being activated. The elastic energy stored in the robot body allows it to complete a repeatable actuation cycle by recovering the SMA automatically after its contraction. With above structures, we demonstrate the walking and climbing ability of this robot with a locomotion speed of 1 mm/s. The climbing of a vertical wall along both the vertical and horizontal directions is achieved.

Keywords:Soft Robot Locomotion, Service Robots, Biologically Inspired Soft RobotsAbstract: This paper presents the design and testing of a soft robot for water utility pipeline inspection. The preliminary findings of this new approach to conventional methods of pipe inspection demonstrate that a soft inflatable robot can successfully traverse the interior space of a range of diameter pipes without the need of adjusting mechanical components. The robot utilizes inflatable soft actuators with adjustable radius which, when pressurized, can mobilize the robot inside the pipe, or anchor it in place. Utilizing a control algorithm for locomotion allows the robot to maneuver through a pipe mimicking the motion of an inchworm. This paper offers an evaluation of the structure and behavior of the inflatable actuators through computational modeling of the material and design, as well as the experimental data of the forces and displacements generated by the actuators. The theoretical results are contrasted to experimental data utilizing a physical prototype of the soft robot. The unique design is anticipated to enable compliant robots to conform to the space offered to them and overcome any occlusions from accumulated solids found in pipes.

Keywords:Biomimetics, Soft Aerial Robots, Soft Robot LocomotionAbstract: Insect-inspired flapping wing micro air vehicles (MAV) have attracted considerable interest due to their potential for agile flight in complex environments. Resonant excitation of the wing flapping mechanism in insects is highly advantageous as it amplifies the flapping amplitude and reduces the inertial power demand. Dielectric elastomer actuators (DEA) produce large actuation strain and their inherent elasticity is ideal for resonant operation. In this work we present a double cone DEA design and characterize its resonant frequency and phase shift to analyze its mechanical power output as a DEA-mass oscillator. Then an artificial thorax driven by this elastic actuator is demonstrated, this thorax design is able to provide a peak flapping amplitude of 63° at a frequency of 18 Hz.

Keywords:Mechanism Design, Soft Robot Locomotion, DynamicsAbstract: Small robot is favorable in diverse application. Dielectric elastomer is soft active material, offering new insight in robotic actuation. This paper describes a lightweight robotic cube driven by a dielectric elastomer resonator (DER). The vibration performance of the DER is experimentally studied and characterized for a fast speed actuation in robotic cube. This robotic cube has an excellent athletic ability. Firstly, without wheel, leg or track, it can locomote rectilinearly at the first mode resonance frequency of DER, with the speed of 0.78 body length per second. Secondly, the robotic cube can change its direction (U-turn) at the second mode resonance frequency of DER. The robotic cube favors simplicity in manufacture and multi-mode locomotion integration controlled by a single actuator at its voltage change.

Keywords:Mechanism Design, Soft Robot Locomotion, Flexible RobotsAbstract: Smart fabrics offer the potential for a new generation of soft robotics, reactive clothing and wearable technologies through the fusion of smart materials, textiles and electrical circuitry. In this work we present a range of smart fabrics and reactive textiles for soft robotics. We investigate conductive stretchable textiles for the fabrication of dielectric elastomer (DE) and electroadhesive (EA) actuators. These include a planar DE actuator, a bending DE actuator, and an EA actuator. The textile DE actuator generated a relative area expansion of 16.4 % under 9 kV while the bending actuator generated a relative expansion of 5 % under 6 kV. The EA actuator generated a shear adhesive force of 0.14 kPa at less than 5 kV. This work shows the feasibility of using conductive fabrics for soft actuation technologies. Conductive textiles have the potential to deliver simple, comfortable, multi-function and wearable soft robotic devices and complete soft robots.

Keywords:Medical Robots and Systems, Flexible Robots, Sensor-based ControlAbstract: Background: Resuscitative endovascular balloon occlusion of the aorta (REBOA), is a life saving intervention employed during heavy internal bleeding in the pelvis and abdomen. A balloon is inserted into the aorta to prevent distal blood flow.

Aim: To develop a system using soft-technologies that permits adaptive interactions in an unpredictable biological environment. A system that acts as a diameter sensor and flow modulation device for catheter based application that can safely interact with humans.

Methods: We hypothesized that the internal pressure of the balloon would rise as it presses against the aortic lumen, thus providing a surrogate marker for diameter. The device constructed measures balloon pressure via a tee junction at the syringe catheter interface. Repeat measurements (ten) for tubes of diameters, 10, 8, 7, 6 and 5mm were obtained giving 50 sets of data. A neural network was created and trained. Unseen data was used to test the network. Blood flow modulation was achieved via a tendon deformable balloon. Deformability was achieved by gluing strings on the internal surface of the balloon.

Results: The diameter sensor showed that pressure peaks were higher in smaller tubes with 7mm showing a peak at 10.9 PSI, 8mm showing a peak at 9.7 PSI and 10mm showing a peak at 8 PSI. The peaks also occurred earlier at 8200, 8600, 8800 ms for 7, 8 and 10 mm respectively. The 5 and 6 mm diameter tubes had higher pressures when compared to the rest of the data for their respective times. The trained neural network made very accurate predictions of the diameter using the test sets with a RMSE of 0.022 (0.22mm). Flow modulation was achieved using strings that pinched the balloon inwards allowing flow of fluid at that point, distal migration of the balloon was avoided.

Conclusion: A portable soft robotic system that accurately measures diameter and allows blood flow modulation was successfully built. The system is simple enough to be incorporated into current catheters with little modification. The first steps towards the development of a bespoke system for haemorrhage control has been demonstrated. Future work will focus on integrating the system with a control loop and testing the system in vivo.

Keywords:Morphological Computation, Biologically Inspired Soft Robots, Evolutionary RoboticsAbstract: Soft robotic arms have gained popularity in the recent years because of their dexterity, robustness and safe interaction with humans. However, since these arms are subject to non-linear mechanics and are intrinsically under-actuated, their control still present many challenges. Octopus arms are one of the most popular biological models for soft robotics. It is known that the octopus reaching movement consists in two steps: (1) the rotation of the arm’s base towards the target, and (2) the extension of the arm to reach the target. From a robotics point of view, the rotation of the base adds one additional degree of freedom to an already hyper-redundant system. Therefore, its role in the effectiveness of the control is ambiguous. In this work, we investigate the role of the base rotation for learning an effective reaching strategy. We conduct numerical experiments based on a mathematical model of the mechanics of the octopus arm in water and a simple neural network enabling to encode the control strategy through optimization learning. The network node corresponding to the base rotation is switched on or off for comparison. We test the reaching success rate with and without base rotation with targets in various positions. The results show that the addition of the base rotation can be highly beneficial or even detrimental, based on the position of the target. Nonetheless, globally the addition of base rotation affects the control strategy and expand the reachable regions.

Keywords:Morphological Computation, Embodied Intelligence, Perception for Soft Grasping and ManipulationAbstract: Sensor morphology is a fundamental aspect of tactile sensing technology. Design choices induce stimuli to be morphologically processed, changing the sensory perception of the touched objects and affecting inference at a later processing stage. We develop a framework to analyze the filtered sensor response and observe the correspondent change in tactile information. We test the morphological processing effects on the tactile stimuli by integrating a capacitive tactile sensor into a flat end-effector and creating three soft silicon-based filters with varying thickness (3mm, 6mm and 10mm). We incorporate the end-effector onto a robotic arm. We control the arm in order to apply a calibrated force onto 4 objects, and retrieve tactile images. We create an unsupervised inference process through the use of Principal Component Analysis and K-Means Clustering. We use the process to group the sensed objects into 2 classes and observe how different soft filters affect the clustering results. The sensor response with the 3mm soft filter allows for edges to be the feature with most variance (captured by PCA) and induces the association of edged objects. With thicker soft filters the associations change, and with a 10mm filter the sensor response results more diverse for objects with different elongation. We show that the clustering is intrinsically driven by the morphology of the sensor and that the robot’s world understanding changes according to it.

Keywords:Morphological Computation, Force and Tactile Sensing, Contact ModelingAbstract: Previously, we have developed an active tactile sensing system that can select sensing modalities based on specific sensing tasks by changing its morphology, named Wrin’Tac. This tactile sensing system is constructed by an integration of actuation (pneumatic actuator) and sensing elements (strain gauge) inside a thin, multi-layered substrate. Under pressurization, the morphology of the substrate surface changes with the appearances of wrinkle. As a result, this device can detect both static load under indentation and dynamic sliding action by using only a single type of sensing element (strain gauge). In this paper, we present a computational model for estimation of the wrinkle’s morphology and prediction of output of embedded sensing elements. The shape of the wrinkle and the posture of the sensing element are evaluated by calculating the height of the wrinkle. The wrinkle’s mechanical change is assessed by ascertaining the stiffness of the wrinkle under vertical indentation by a spherical indenter. The output voltages of the sensor are calculated by the proposed model and the experimental values have an error of less than 10%, which validates the accuracy of the proposed model. We also pointed out the role of the wrinkle’s morphology to the sensor’s sensitivity, implying that this sensing system may select suitable sensitivity for specific sensation tasks. This work is expected to pave a way for assessing the role of morphological change to tactile sensation, and development of soft active tactile sensing systems.

Keywords:Multifingered Hands, Robot Safety, Sensor-based ControlAbstract: We present the hardware design and fabrication of a soft arm and hand for physical human-robot interaction. The six DOF arm has two air-filled force sensing modules which passively absorb impact and provide contact force feedback. The arm has an inflated outer cover which encloses the arm's underlying mechanisms and force sensing modules. An internal projector projects a display on the inside of the cover which is visible from the outside. On the end of the arm is a 3D printed hand with air-filled, force sensing fingertips. We validate the efficacy of the outer cover design by bending the arm to reach out and grasp an object. The outer cover performs as intended, providing enough volume and range of motion for the arm to move, and stretching at the elastic relief features in the cover. We also validate the hand design by implementing a grasping algorithm in which the fingers follow a closing trajectory, make contact, then maintain a given range of fingertip pressure. Using this algorithm, the hand is able to gently grasp a soft object.

Keywords:Multifingered Hands, Soft Gripper and End-EffectorsAbstract: This study presents a novel four-fingered robotic hand to attain a soft contact and high stability under disturbances while holding an object. Each finger is constructed using a tendon-driven skeleton, granular materials corresponding to finger pulp, and a deformable rubber skin. This structure provides soft contact with an object, as well as high adaptation to its shape. Even if the object is deformable and fragile, a grasping posture can be formed without deforming the object. If the air around the granular materials in the rubber skin and jamming transition is vacuumed, the grasping posture can be fixed and the object can be grasped firmly and stably. A high grasping stability under disturbances can be attained. Additionally, the fingertips can work as a small jamming gripper to grasp an object smaller than a fingertip. An experimental investigation indicated that the proposed structure provides a high grasping force with a jamming transition with high adaptability to the object's shape.

Keywords:Optimizatoin and Optimal Control, Hydraulic/Pneumatic Actuators, Soft Gripper and End-EffectorsAbstract: Soft robots demonstrate interesting possibilities of handling fragile and highly deformable objects without complex and accurate control. So far, the design of soft robots mostly rely on designer's intuition and trail-and-error method which is not efficient and therefore hinders the wide applications of soft robots. In this paper, we presented a way to investigate the optimal chamber design of a bellow-type soft actuator using Abaqus and Isight software. The finite element (FE) model of the actuator was developed in Abaqus with two design variables. The model was then imported into Isight and two objective functions of maximizing bending deformation and contact force were implemented. The optimal parameters were found to be at the boundaries of the predetermined parameter sets. Four kinds of actuators, having parameters of the initial guesses, optimal values, and two other optional sets, were fabricated and experimentally tested. Good agreements were achieved. Two-fingered grippers were constructed using different actuators and grasping tests were performed on defrozen broccolis. Results showed that using the optimized actuators required less air pressure to handle the same targets.

Keywords:Physically Assistive Devices, Wearable Robots, Human-Centered RoboticsAbstract: We present a high strength artificial muscle for inclusion in an orthotic device that can deliver power at the knee joint with the aim of improving knee flexion in people with reduced mobility. The bubble artificial muscle (BAM) was developed by adapting traditional pleated pneumatic artificial muscles to achieve high contraction and tensile force. Initial gravimetric evaluation of a single BAM was performed, achieving a contraction of 23.7% while lifting a mass of 2.5 kg (over 100 times the mass of the actuator). To demonstrate the actuator’s suitability for an orthosis, a device consisting of three parallel BAMs was tested with a physical pendular leg model based upon a human leg. A maximum knee flexion of 47.25 degrees was achieved, about 70% of the peak knee flexion of the average of young healthy subjects (68 degrees). 8.19 Nm of torque was delivered during testing, which is approximately 33% of the knee flexion moment during swing phase of a gait cycle. This high moment is achieved despite the low mass of the device (206.6 g). This work shows the suitability of BAMs for wearable orthotic devices such as soft assistive suits, where softness, lightness and high stress and strain are essential.

Keywords:Rehabilitation Robotics, Wearable Robots, Biologically Inspired Soft RobotsAbstract: Soft robotic gloves have shown great potential in accelerating the rehabilitation process of individuals with hand pathologies. However, most of the existing soft assistive devices allow a single degree-of-freedom (DoF) movement for each finger while independent motion of finger joints plays a crucial role in hand rehabilitation. Trying to address these challenges, a novel fishbone-inspired soft actuator with multi-DoFs is proposed in this article for the first time, to the best knowledge of the authors, and a preliminary soft glove is developed. With the assistance of the glove, the Metacarpophalangeal (MCP) and the proximal interphalangeal (PIP) joints of human fingers can bend or extend independently. In this paper, the basic concept of the actuators is illustrated in detail and the structural parameters are determined with FEM models. Additionally, several groups of experiments are conducted to demonstrate the varied motion patterns of the actuators and the bending curvature of each segment in different patterns is calculated. Lastly, the efficacy as well as the dexterity of the proposed soft glove is further validated by performing complicated gestures and conducting functional grasping tests.

Keywords:Sensor-based Control, Hydraulic/Pneumatic Actuators, Flexible RobotsAbstract: This paper reports on a piezoresistive strain sensor that uses vertically aligned carbon nanotube (CNT) filler elements which are embedded in a rubber matrix. Compared to previously used conductive filler elements, vertical CNTs can be patterned using lithography, making it possible to scale down the sensor footprint into the micrometer range. This technological advancement is instrumental for developing intelligent soft microrobots with embedded flexible sensors. We compare vertical CNTs and carbon black as filler elements, where newly developed lithographic production techniques are applied to shape a generic strain sensor topology that is compatible with the majority of planar inflatable microactuators. This research shows a significant improvement in sensor linearity by using vertical CNTs as filler elements over carbon black. Further, a lithographically fabricated strain sensor has been successfully embedded in an elastic inflatable bending microactuator with outer dimensions of 5.5x1x0.06mm3. The full lithographic production process to create this actuator is described in this paper, together with its characterization under a static pressure input.

Keywords:Soft Gripper and End-EffectorsAbstract: In this paper, we present a compliant robotic gripper, Edgy-2, with 4-DOF dexterity, enabling four grasping modes: parallel grasping, power grasping, finger-tip pinch and fully-actuated grasping. The robotic finger is based on soft-rigid-hybrid structures, combining fiber-reinforced soft pneumatic actuators with rigid joints, which exhibit reliable structural rigidity and grasping robustness while maintaining excellent adaptability and inherent compliance. With both grasping dexterity and grasping robustness, the Edgy-2 achieves excellent grasping reliability with various daily objects, from a fragile cherry to a 2 kg water bottled water. The relationship of design parameters and grasping strength is presented with analytical models. The performance of a prototype Edgy-2 is verified by dedicated experiments. The proposed hybrid dexterous grasping approach can be easily extended into different end-effector designs according to application requirements. The proposed mechanism for grasping provides excellent human-robot interaction safety and reliability.

Keywords:Soft Gripper and End-Effectors, Biologically Inspired Soft Robots, Force and Tactile SensingAbstract: Locking two surfaces with minimum normal force may result in safe grasping of objects in soft robotic hands. This paper presents a preliminary approach on design and analysis of a bio-inspired soft pad that enhances the adhesion with the environment by morphological design of its surface at micro-scale. The design principle is originated from the biological wet attachment of a tree-frog toes with the surrounding environment, caused by capillary force and surface tension of a secretion film between the toe and the surface. Especially, the tree-frog's toe has a network of polygonal cells (or blocks) with grooves among them, which act as liquid reservoirs and capillary tubes. We conducted some analysis on this wet adhesion principle, showing that total normal force increases with the grooved pattern compared to the that of the flat one in wet condition. We then fabricated a micro-patterned mold, using e-beam technology, for casting grooved surface onto a silicon substrate. We also conducted preliminary investigation of the adhesion strength of the fabricated soft pad with measurement of normal force under wet and dry condition. This is the first time wet adhesion was considered in soft robotic grasping, and this research is expected to be applied in wet and high-moisture environment.

Keywords:Soft Gripper and End-Effectors, Compliant Joint/Mechanism, Mechanism DesignAbstract: In this paper, a systemic approach to design and fabricate a multimaterial soft gripper is proposed. Driven by pneumatic pressure, the soft material inside the gripper acts as integrated actuator and the relatively hard material provides support for its soft body. Because of a large design space, it’s hardly to design a multimaterial structure by intuitive or biomimetic approaches. Herein, this structural design problem is tackled by topology optimization approach, where each gripper finger is modeled as a compliant mechanism to achieve its maximum bending deflection. Considering the fabrication process, the soft material structure is preserved unchangeable during the optimization process. Thereafter, the optimized hard material is fabricated through 3D printing and the soft material is created by molding. Characterization experiments show that each gripper finger can undergo 32° bending deformation and exert 0.54N grasping force under 0.05MPa actuation pressure. Moreover, the multimaterial soft gripper can sustain more than 1000 working cycles and grasping a variety of objects ranging from tiny regular skews to large and delicate sunglasses. The proposed design and fabrication approach is freely extendable to soft robots by forming the corresponding optimization model, and stands as a gateway toward high-performance multi-material soft robots.

Keywords:Soft Gripper and End-Effectors, Morphological Computation, Biologically Inspired Soft RobotsAbstract: Recently developed soft pneumatic actuators (SPAs) powered by negative pressure have demonstrated great potential in the future of soft robotics for their high strength, intrinsic safety, low weight, and often simple design. The majority of these have only been demonstrated to provide linear force and motion profiles, however, despite the general prevalence of bending actuators common to positive pressure powered SPAs. The benefits of such bending type SPAs follow from the direct production of moment and angular motion that are highly desirable for diverse robotic applications and activities, which allows more simple design of soft robots with complex motion behavior. Following this motivation, a new vacuum powered bending actuator is developed here as an extension of a previously presented vacuum powered actuator, the V-SPA, which features simple, lightweight material construction and rapid fabrication. Leveraging these attributes, an empirical study of a new Coil V-SPA performance is conducted across a spectrum of eight actuator prototypes. The force, speed, and stiffness of the actuators are characterized, and a generalized design metric, the Geometric Compression Ratio (GCR), is defined to quantify the relationship between physical geometric parameters of Coil V-SPAs. Finally, the results of testing reveal the new low-inertia actuator is capable of high-speed, and high-bandwidth motion, up to 0.97 m/s and 1.58 Hz, respectively.

Keywords:Soft Gripper and End-Effectors, Soft Humanoid RobotsAbstract: In this study, a cable actuated soft gripper is used to analyze the effects of finger material properties on grasping forces. The gripper design and the fabrication of soft fingers using materials of varying elastic moduli are presented. A model is developed to predict the holding force of each gripper configuration and predictions are compared to results from grasping experiments. The experiments show a decrease in grasping force with increasing stiffness when normalized for the cable tension as predicted by the model. %This indicates a trade-off between finger compliance, generally seen as advantageous for adaptability in manipulation tasks, and effective grasping.

Keywords:Soft Robot Locomotion, Applied Mathematics for Soft Robotics, Control Architectures and ProgrammingAbstract: Soft material robots have potential for deployment in dynamic environments, e.g. search and rescue operations, owing to their impact resistance and adaptability. However, these advantages are accompanied by challenges of robot control and surface identification. The continuum, soft material robot body interacts uniquely with different environments e.g. a smooth table or a rough carpet. These interactions with the surface can be discretized and modeled using graph theory. This representation allows the robot to learn from its surroundings and generate environment-specific locomotion control sequences. Here, simple cycles of individual graphs are analogous to periodic locomotion gaits of the soft robot. Inversely, provided the knowledge of different environments (captured in the individual graphs), the robot has ability to optimally identify the environment through experimentation and interaction. This paper presents a method for soft robots to a) optimally learn the environment and b) determine optimized movements for identifying the surface of locomotion by utilizing the information from previously experienced environments. The optimized movements are identified as arcs, paths and simple cycles that yield the most contrasting costs. The surface identification is performed by analyzing the locomotion cost differential between the experienced surface interaction and that of a previously known environment. The learning and control algorithms (Eulerian path, simple cycles) are `arc-centric' i.e. focus on traversing arcs. Whereas surface identification algorithms are `node-centric' i.e. focus on traversing nodes (simple paths).

Keywords:Soft Robot Locomotion, Marine Robotics, Biologically Inspired Soft RobotsAbstract: This paper presents the results of single pulsation tests aimed to evaluate the performance of a Hoberman sphere mechanism as an underwater jet propulsor. The tests were carried out in a fish tank and the position of the robot was visually tracked to estimate the speed and the contraction kinematic. Results suggest that, due to the great volume variation allowed by the Hoberman sphere, this system can reach similar performances in term of speed with respect to previous solutions, while it can improve the generated thrust.

Keywords:Soft Robotics Inspired Biology, Biologically Inspired Soft RobotsAbstract: Inspired by teleost fish scale, this paper investigates the possibility of implementing stiffness control as a new source of robots dexterity and flexibility control. Guessing about the possibility of biological scale jamming in real fish, we try to understand the possible underlying actuation mechanism of such behavior by conducting experiments on a Cyprinus carpio fish skin sample. Bulking tests are carried out on an encapsulated skin sample, in thin latex rubber, for unjammed and vacuum jammed cases. For the first time, we observed biological scale jamming with very small hysteresis due to the unique scale morphology and jammed stacking formation. We call this unique feature "Geometrical Jamming" where the resisting force is due to the stacking formation rather than the interlocking friction force. Inspiring by this unique morphology and helical arrangement of the scale, in this research, we investigate different possible design and actuation mechanisms for an integrable scale jamming interface for stiffness control of continuum manipulators. A set of curved scales are 3D printed which maintain a helix formation when are kept in place and jammed with two thin fishing steel wires. The non-self locking jagged contact surfaces replicate inclined stacking formation of the jammed fish scale resulting in the same reversible low hysteresis characteristics, in contrast to the available interlocking designs. The effectiveness of the designs are shown for uniaxial elongation experiments and the results are compared with similar research. The contact surfaces, in our design, can be lubricated for further hysteresis reduction to achieve smooth, repeatable and accurate stiffness control in dynamic tasks.

Keywords:Soft Robotics Inspired Biology, Biomimetics, Biologically Inspired Soft RobotsAbstract: This paper presents a lightweight caterpillar-inspired soft-bodied robot that produces crawling locomotion on a stick. The significant features are passive-grip/active-release opposable legs and dual elastic arch structure to couple the segment contraction and the leg opening. These actuations are driven by a shape memory alloy (SMA) coil attached along the body axis. The mechanical design allows the robot to hold the unstable substrate without energy consumption. We find that adequate activation time lag between the legs/segments exists but the system is not sensitive to the parameter changes thanks to the softness of the body. The robot can build very cheap (less than 30 US dollars) to 3d-print using hard and rubber-like materials together, which doesn't require any assembly labor to build the body.

Keywords:Tendon/Wire Mechanisms, Soft Gripper and End-Effectors, Flexible RobotsAbstract: In this paper, an iterative learning control scheme for a trajectory tracking task using a one-DOF joint manipulator which is driven by multiple antagonistic fishing line artificial muscle actuators is proposed. The fishing line actuator is one of the soft actuators made by coiling and heating a twisted polymer fiber. It has attracted attention from those who would develop soft robotic devices because it is soft, light, and low-cost. It, however, has several drawbacks, e.g. output force limitation, strong nonlinearity, or energy efficiency, etc. To cope with these drawbacks, firstly a one-DOF manipulator driven by multiple antagonistic actuators is proposed to enhance its output force, and the energy efficiency is analyzed to investigate the relationship between the energy consumption and a number of activated fishing line actuator. Next, an iterative learning control scheme to accomplish a trajectory tracking task by the one-DOF manipulator is proposed to improve its control performance even though under the existence of unknown nonlinearities. The effectiveness of the proposed control scheme is demonstrated through several experiments.

Keywords:Underactuated Control of Soft Robots, Soft Robot Locomotion, Biologically Inspired Soft RobotsAbstract: A key advantage to Fluidic Elastomer Actuators (FEA) is that they permit easy fabrication of robots capable of sophisticated manipulation and mobility. This advantage arises primarily from the continuous stretching and relaxation of elastomeric material that defines an active degree of freedom (DOF), prescribed during the manufacturing process. While the low elastic moduli of the soft material allows for infinite passive DOFs, each active DOF typically requires a valve and/or pump. On-board valving adds weight and size to the robots, and off-board valving requires tubing that imparts resistance to flow and requires higher pressure differentials for reasonable actuation velocities. In contrast to these methods, the work presented here exploits fluidic resistance in poroelastic foam actuators to create a traveling wave using only a single valve and pressure inlet. This concept is evaluated with respect to foam volume and fluid viscosity, and further demonstrated in a three-legged robot capable of millipede-inspired locomotion. The robot is capable of traveling at ~1.1 mm/s, with individual legs (closest to the inlet) extending 41.28, 27.36, and 12.95 mm. These results represents an important step towards increasingly complex behavior in soft robots that remain simple to fabricate and control.

Keywords:Wearable Robots, Formal Methods for Soft Robotics, Rehabilitation RoboticsAbstract: this paper presents a low profile stretch sensor for integration into soft structures, robots and wearables. The sensor mechanism uses a single piece of highly flexible and light weight optical fibre and is based on the notion that bending an optical fibre modulates the intensity of the light transmitted through the fibre, a technique often referred as macrobending light loss. In this arrangement, the optical fibre originates from sensor’s electronic unit, passes through a stretchable encasing structure in a macrobend pattern, and then loop back to the same unit resulting in a simplified electrical and optical design; the closed optical loop allows for no electronics at one end of the sensor making it safe for human robotics applications, and no optical interference with the external environment eliminating the need for complex conditioning circuitries. Of particular interest of the soft robotics community, the ability of this custom macrobend stretch sensor to flexibly adapt its configuration allows preserving the inherent softness and compliance of the robot which it is installed on. Our experimental results indicate that the optical fibre’s bending radius is the dominant design parameter for sufficiently complex patterns, a finding that can facilitate generalisation of the sensing methods across different scales. The measurement performance of the mechanism and its impact on the stiffness of the encasing structure is benchmarked against a custom calibration and testing system.

Keywords:Wearable Robots, Prosthetics and Exoskeletons, Haptics and Haptic InterfacesAbstract: Variable stiffness technologies help to solve the conflicting requirements of strength, comfort, and safety in soft exoskeletons. Here, we propose a modular variable stiffness strip based on layer jamming as a mechanical solution to constrain users’ degrees of freedom and/or to implement wearable anchor points. Equipped with integrated capacitive strain sensors in the longitudinal direction, the strip is 30 mm wide and 3 mm thick and has a modular design that enables its adaptability to different morphologies and force requirements. If negative pressure in the order of tens of KPa is applied, the strip undergoes a stiffness change by a factor of 600, thus ranging between stretchability typical of elastane and inextensibility up to a maximum resisting force of 60 N. The versatility of the strip is shown by integration in an upper body exosuit.

Keywords:Wearable Robots, Rehabilitation Robotics, Physically Assistive DevicesAbstract: In this study, we present the design and development of a shoe outsole with active soft suckers which demonstrates a better shear resistance to prevent slip/fall of the user. The proposed design of the shoe outsole is layered by a multi-material structure with a soft suckered pattern connected to a vacuum pump (-0.8 bar). The sucker function can increase the normal force at the shoe/ground interface and enhance the frictional properties of contact area, which helps assuring a secured walking both in dry and wet surface condition. The developed shoe prototypes were characterized on different ground conditions with varying vertical load assuming the applied vertical force in human locomotion. The maximum shear resistance (≥50 Kg force) was recorded for suckered outsole that was higher than the shear resistance (≥0.9 Kg force) of normal outsole of a commercial product. The experimental results are promising in the direction to have a firm grip with suction at varying surface condition to prevent fall/slip while walking with the balance of shear force and frictional force.

Keywords:Wearable Robots, Rehabilitation Robotics, Prosthetics and ExoskeletonsAbstract: This paper presents the design and evaluation of a soft hand exo-sheath integrated with a soft fabric electromyography (EMG) sensor for rehabilitation and activities of daily living (ADL) assistance of stroke and spinal cord injury (SCI) patients. This wearable robot addresses the limitations of the soft robot gloves with design considerations in terms of ergonomics and clinical practice. Its features include: this exo-sheath is based on electric actuation and has been designed to be compact and portable. It reduces the shear force and avoids kinematic singularity comparing with tendon-driven soft gloves as their tendon routings are typically in parallel with individual fingers. Disparate from conventional robotic gloves, this design optimizes a bio-inspired fin-ray structure to enhance the hand proprioception as the palm is not covered by wearable structures. With a novel self-fastening finger clasp design, wearers can self-don/doff the exoskeleton device simplifying ADL assistance. To develop more intuitive control interface, a soft fabric EMG sensor has been developed to understand human intentions. The functionality of this soft robot has been demonstrated with experimental results using the low-level position control, kinematics evaluation and reliable EMG measurements.

Keywords:Biologically Inspired Soft Robots, Biomimetics, Soft Robotics Inspired BiologyAbstract: Robotic agents that are accepted by animals as conspecifics are very powerful tools in behavioral biology because of the ways they help in studying social interactions in gregarious animals. In recent years, we have developed a biomimetic robotic fish lure for the purpose of studying the behavior of the zebrafish Danio rerio. In this paper, we present a series of experiments that were designed to assess the impact of some features of the lure regarding its acceptance among the fish. We developed an experimental setup composed of a circular corridor and a motorized rotating system able to steer the lure inside the corridor with a tunable linear speed. We used the fish swimming direction and distance between the fish and the lure as a metric to characterize the level of acceptance of the lure, depending on various parameters. The methodology presented and the experimental results are promising for the field of animal--robot interaction studies.

Keywords:Marine Robotics, Force and Tactile Sensing, Biologically Inspired Soft RobotsAbstract: The design, calibration and testing of an experimental rig for measuring 2-DOF unsteady loads over aquatic robots is discussed. The presented apparatus is specifically devised for thrust characterisation of a squid-inspired soft unmanned underwater vehicle, but its modular design lends itself to more general bioinspired propulsion systems and the inclusion of additional degrees of freedom. A purposely designed protocol is introduced for combining calibration and error compensation upon which force and moment measurements can be performed with a mean error of 0.8% in steady linear loading and 1.7% in unsteady linear loading, and mean errors of 10.2% and 9.4% respectively for the case of steady and dynamic moments at a sampling rate of the order of 10 Hz. The ease of operation, the very limited cost of manufacturing and the degree of accuracy make this an invaluable tool for fast prototyping and low-budget projects broadly applicable in the soft robotics community.

Keywords:Soft Robotics Inspired Biology, Soft Robot Locomotion, Soft Gripper and End-EffectorsAbstract: Soft robots have several promising features for underwater manipulation, e.g., safe interaction with surroundings, lightweight, low inertia, etc. In this paper, we proposed a method for the inverse kinematics of the soft manipulator that can move in the three-dimensional space. By controlling the two bending segments to move with opposing curvatures and one elongation section to move up and down, our method enables the real-time solution of the inverse kinematics and allows the tip of the manipulator executing point-point movements in three dimensions. We performed the trajectory planning ability of the soft manipulator following the straight line and circle paths. Furthermore, we investigated the hydrodynamic functions of the soft manipulator underwater including forces, and the wake flows when the soft arm stroke at different amplitudes and frequencies. We found that the hydrodynamic force (<1N) and the torques (<0.1Nm) were quite small during locomotion-- which led to a negligible inertial impact on the underwater vehicle compared to the traditional rigid underwater manipulator. Finally, we demonstrated that the soft manipulator successfully picked and placed sea animals at 10m depth.